Penance Priest

It seems to be a good time for a review of this
class-defining talent. I’ve seen many questions about it recently and tons of
misunderstandings about how it works. So I started writing a little “hey guys,
don’t forget!” piece. It kind of got out of hand. Honest…this really did start
out as a simple article, but once I got going, I realized how much there is to
talk about! It’s a simple talent, but once you start thinking it through,
you’ll see how valuable it is to understand its nuances and implications.

Also, as you’ll see, you can’t really discuss Divine Aegis
without including Inspiration and Grace in the mix. They’re all secondary effects
of your healing spells.

In fact, I confess. This isn’t an article about Divine
Aegis. It’s really about taking your understanding of discipline to a higher
level.

There’s a little bit of math in here, but it’s junior high
school stuff. No rocket science, I promise.

You can stack DA bubbles up to a max of 10k hp on a level 80
friendly. That was big news; before that change, DA was binary (on or off), and
confusion was rampant about how it worked in practice. (I.e., what happens when
you crit several times in a row?) The 3.1 version of Divine Aegis also takes
into account overheal, which makes it just… mwah.

I’ll be using that word (“binary”) quite a lot. It’s just
fancytalk for an on/off switch, something with no gray area. Shadowform is
binary (you’re in it or you’re not), as is pregnancy, a coin-flip, and whether
or not you’re Chuck Norris. There is no gray zone in binaryland.

Detour!

Here is the definition of a very related talent, Inspiration, which you are not
allowed to skip, ever, ever, for any reason, go Inspiration or go home:

Your Flash Heal, Greater Heal,
and Penance spells have a 100% chance to bless the target with Grace, increasing
all healing received from the Priest by 3%. This effect will stack up to 3
times. Effect lasts 15 sec. Grace can only be active on one target at a
time.

Only a few spells will proc Grace, but once it’s up, the
healing bonus will benefit all of your healing spells. (But no one else
benefits; just you.)

I haven’t forgotten that this is supposed to be an article
about Divine Aegis. Sort of.

Secondary healing-effect
matrix

I wish I had a catchier name for it. Let me know if you come
up with one.

Let’s look at which of these secondary effects can be
applied when you cast a healing spell. Entries in the table marked “crit%” will
only proc when you crit, so not every cast of Flash Heal will proc Inspiration,
for example. A “yes” in a column means every cast will proc the effect,
not just criticals.

Divine Aegis

Inspiration

Grace

Flash Heal

crit%

crit%

Yes

Greater Heal

crit%

crit%

Yes

Penance

crit% (*)

crit% (*)

Yes (*)

Binding Heal

crit% (*)

crit% (*)

No

PoM

crit% (*)

crit% (*)

No

PoH

crit% (*)

crit% (*)

No

PW:Shield

crit% (glyph)

No

No

Renew

No

No

No

Entries with an asterisk (*) have multiple chances to proc. Other
than Penance, these are multi-target heals, so each target will only get at
most one application of each effect at a time. Penance, however, can proc
multiple times on the same target.

Power Word: Shield cannot proc Divine Aegis, although the
heal from the Glyph can. The
DA bubble will be 30% of the 20% heal from the glyph. It’s not much, but it’s
there. (Also, it's currently bugged so that it only procs DA on shields
you cast on yourself.)

Remember the different natures of these three effects. This
is important!

Inspiration is binary; it’s either up on your
target or it ain’t.

Grace is a three-step platform. It has zero, one,
two, or three stacks on your target, for 3%, 6%, or 9% increased healing.

Divine Aegis is a gradual scale from zero to 10k.

You know what? Just because I think it’s really important,
I’ll make a graph.

Divine Aegis scales with ____

Quick! Fill in the blank.

If you said “crit,” you’re right!

If you said “spell power,” you’re right!

If you said “haste,” you’re still right, but the
relationship is a little more complex. Haste is one of the best stats for a
tank-healing disc priest, and certainly speeding up your spell-casts will speed
up the application of DA bubbles. But spell power and crit will be easier for us
to analyze, frankly, and haste’s effect on DA is more diffuse. We’re not going
to get into issues of boss-swing timers, or how fast you can build up DA to its
maximum vs. how fast a boss can clobber that bubble. For now, we’ll focus just
on maximizing the DA bubble through spell power and crit, and try to assess
which stat will have a bigger impact on your DA mitigation.

Average DA per cast

Let’s start with some basic calculations to figure out an
average amount of DA mitigation you get for every spell you cast. We’ll use
Flash Heal as a reference.

The last line is the one that’s the most interesting.
Average DA per cast shows the average amount of bubbly protection you get per
cast. You won’t get a DA bubble on every cast, of course. This is just an
average.

So, how do you raise your average DA per cast? More spell
power, and/or more crit. Our next job is to figure out which is better, if your
goal is to maximize this mitigation effect.

Spell power vs. crit

If your base Flash Heal hits for 5000, that means you’ll
crit-heal for 7500. When you crit, a DA bubble will be created for 30% of that
amount, or 2250. And if you have a 40% crit rate, your average DA per cast will
be 900. That means: on average, every time you cast Flash Heal, you will see
900 hp of DA mitigation applied to your target. To build up 10k of mitigation
(the max we can have at any one time), it will take approximately eleven casts
of Flash Heal. Odds are some of that DA bubble will have been chipped away in
the time it takes you to cast that many spells.

Now, consider how much your spells benefit from stacking
spell power versus stacking crit. Again, I’ll be using Flash Heal as an
example. I’m definitely going to ignore the bonus crit from Improved Flash Heal, and I will
also ignore bonus healing effects such as Grace and Guardian Spirit.

We’ll take a nicely-geared ICC priest as our baseline, then
see what happens when we add a crit gem versus what happens when we add a spell
power gem.

The baseline priest will have 3400 spell power and 40% crit
rating (raid buffed). Priest “A” will add a single smooth king’s amber; priest “B”
will add a single runed cardinal
ruby. Let’s peek at what happens, shall we? We turn to Zusterke’s excellent
Spell Calculator,
which, while it’s a work in progress, is awesome.

Baseline

With crit gem

With SP gem

Flash Heal

4972

4972

4991

Crit heal amount

7458

7458

7486.5

Avg FH amount

5966.4

5977.2

5989.2

DA amount

2237.4

2237.4

2246.0

Avg DA per cast

894.96

904.7

898.4

Total Avg Heal + DA

6861.4

6881.9

6887.6

WHOA NUMBAHS!! Let’s go through them slowly.

The first three rows show how much your Flash Heal hits for,
not including Divine Aegis. The base heal, the crit heal, and an average that
includes your crit rate. So our baseline priest will see an average Flash Heal
of 5966, which assumes that 40% of his casts will crit. The average heal amount
is in the blue-tinted row.

The next two rows show how much DA mitigation we can expect.
The first row, “DA amount,” shows how much of a DA bubble you’ll see when you
crit. The next row, tinted orange, shows the average amount of DA per cast,
which we discussed above.

If you add the two tinted columns together, you’ll get the
total amount Flash Heal will hit for, including DA mitigation. This total is in
the dark gray row.

As you can see, using a crit gem will increase the size of
your DA bubble more than it will if you use a spell power gem. (This is in the
orange row.) However, the spell power gem will increase your average heal amount
more than the crit gem will (the blue row).

The net effect? Both crit and spell power will benefit you. Crit
has a bigger effect on DA, while spell power has a bigger effect on your base
heal. Overall, spell power is more powerful.

Chances to proc

In every discussion I’ve seen about Greater Heal, someone
makes the point that two Flash Heals have more chances to proc Divine Aegis
than a single Greater Heal. Do you see the flaw in that thinking?

I sure hope so! DA is not binary. It scales. So while GH
takes twice as long to cast as FH, it also has twice the average DA per cast. Over
the long haul, they will create very similar amounts of DA mitigation. One
will create smaller shields more often, the other will create fewer, larger
shields.

(That’s a quickie generalization that doesn’t take into
account Divine Fury or your use of Borrowed Time to accelerate GH, nor does it
take into account the crit bonus from Improved Flash Heal. I’m merely
debunking the idea that “chance to proc” is relevant at all when it comes to
Divine Aegis.)

The other two secondary effects (Inspiration and Grace) both
work on a chance-to-proc basis. Inspiration is binary, and can be applied by
any direct heal. Grace is stair-stepped. So if you need to apply Grace quickly,
you need to cast more spells (or use Penance for a triple-shot).

Here’s that graph again! So simple, but it shows so much.

Smooth vs. spiky DA

Here again is our formula, which illustrates how DA scales
with spell power and crit rating.

Average DA per cast = (base heal
size) * 1.5 * 0.3 * (your crit rate)

As a thought experiment, I’m going to go to the lab and create
two Frankenpriests. The first one will be monstrously oversized in the spell
power department, but barely have any crit rating at all. This means he will
almost never crit, but when he does, the DA bubble will be tremendous because
of his super-sized spell power. Spiky DA.

Frankenpriest #2 will have insane amounts of crit, but just
a tiny bit of spell power. He’ll be critting on every cast, but each DA bubble
will be small. Smooth DA.

Over the long term, the DA protection these two deformed
priests provide might very well be equal, or close to it. However, Frankenpriest
#1 will be creating huge bubbles (rarely), and Frankenpriest #2 will be
creating a large number of tiny bubbles.

Which is better? Well, as long as you’re not overshooting
the 10k cap (in between boss swings), either should be fine. Just get your DA up
as high as you can, as quickly as you can.

But certainly having a higher crit rate is one way to take
the RNG out of the equation. If you had 100% crit, you would never wonder if
you got a DA bubble. You’d have one every time. So the higher your crit rate,
the less of a factor RNG will be for your tank heals. And we all know that
bosses don’t kill tanks; RNG kills tanks.

So in a sense, the smoother DA profile (higher crit rating)
is better for maximizing your mitigation. Marginally. If you go telling
anyone I just advised you to stack crit, I will deny it vehemently. Because
tank healing is not only about Divine Aegis. If at any point your tank’s green
bar dips below 100% -- and it certainly will – the priest with more spell power
will be helping more. Go back up to the blue row in my chart above. Spell power
is still the way.

Short story: Get tons of crit on your gear, and gem for
spell power.

In sum

I’m exhausted! We just covered an entire semester of Disc
Priest University in under 2500 words. Your summary is this:

Divine Aegis is good.

It scales with spell power and crit rating.

DA scales better with crit than with SP, but overall, you benefit more from SP than from crit.

DA protection is not binary; it can scale up to 10k of mitigation at any time.

(8) Comments

Excellent post Prof. P! I was able to follow along quite well and saw that the maths match my mental gymnastics for why what was happening was. The summary and a link to the full article has been shared with my fellow guildies :)

Lovely post! I'm happy to see Divine Aegis get some attention. The information is very helpful as a refresher for shield blinded discipline priests and thorough for starter priests as well. As such, I added the article link to the Discipline Welcome Basket that I keep. It's good to keep track of gems like these for when people need answers later!